We would like to thank Dr. Grey and colleagues for their comments. There was no overall benefit of vitamin D supplementation for time to COPD exacerbation or exacerbation rates in the clinical trial by Lehouck and colleagues (1). However, when a post hoc analysis suggests a possible clinical benefit of vitamin D supplementation, with reduced exacerbations for the 20% of the population with severe vitamin deficiency at baseline (30 of 150 patients followed for 1 year), it would be worthwhile to evaluate whether these findings stand up internally to further statistical scrutiny, and whether they are reproducible.